We have the same dictionary, I think ^^ Those were the definitions I got, too, but just about every time I've seen the word used in anime or manga, it's referring to long-time close friends. It's interesting especially because I would have expected nakama (I'm pretty sure Yuugi-tachi usually refer to one another as nakama, though I think Yuugi might call Jounouchi his shinyuu at one point...) There's an implied intimacy to shinyuu that surprised me.